Electronics, Robotics and Automotive Mechanics Conference 8 MPEG-4 AVC/H.4 AND VC- CODECS COMPARISON USED IN IPTV VIDEO STREAMING TECHNOLOGY Alejandro A. Ramírez-Acosta, Mireya S. García-Vázquez, Juan Colores-Vargas Dpto. R&D, PILIMTEC, Châteaugiron, France Instituto Politécnico Nacional-CITEDI, Tijuana, México alramirez@yahoo.fr, mgarciav@citedi.mx, colores@citedi.mx Abstract Thanks to the permanent evolution of codecs for video and to the coding algorithms, every time with better performance, the television has found a new way of transmission across Internet. Taking into account these evolutions, the performance of the most commercial codecs based on MPEG-4 AVC/H.4 (RealNetworks, Apple) and VC- (Microsoft) standards is analyzed in this article. These codecs are the solutions nowadays for the diffusion of the television through IP network using video streaming technology. The codecs analysis is based on the evaluation of the main parameters that this technology requires. Also, the video streaming technology and its scheme is described.. Introduction This era has been characterized by digitization and convergence of telecommunications, media and information technology. Today, the maturity of technology allows to see, to transmit, to process, and to store the video signal for different platforms. In addition, it enables the interaction with video contents. Due to the explosive growth of the Internet and increasing demand for multimedia information on the web, streaming video [,,3] over the Internet has received tremendous attention from academia and industry [4]. The major inconvenience to video streaming technology when playing real time video is that the bandwidth requirement is directly proportional to the quality and resolution of images. In other words, at a higher quality level of video, more bandwidth is consumed at a given frame rate. For an ADSL connection [], the bandwidth would be easily saturated trying to transmit a non compressed video over internet. Therefore, in order to maximize bandwidth utilization, it is indispensable to use video compression algorithms. Indeed, an efficient data transmission can be ensured relying on specific software components, called codecs (encoder / DECoder) [], whose main tasks are: (i) encoding and compressing the raw video stream coming from an acquisition device; (ii) decoding and expanding the compressed file to rebuild the original video. Some of them are used within several applications from videoconferencing to surveillance and video on demand (VoD) [,,7]. The aim of this paper is to show and to discuss the performance of three principal commercial proprietary codecs used in the video streaming technology, analyzing them and evaluating them under the principal parameters determined by this technology. In this article, section presents briefly an overview of the video streaming technology and its principal parameters. The methodology used for the evaluation of the codecs is the subject of section 3. Section 4 describes the comparative results of the performance of the codecs. Section gives the conclusions of this comparative analysis.. Video streaming technology The term streaming [,,3] represents a bundle of technologies that enable the PC or set top box for IPTV (STB-IPTV), to deliver audio, video, and other media files in real-time, with no download wait over the internet. The content is read while it is stored in a video buffer. The streaming is base on a client-server model. The general principle of this set of technologies is that the audio/video content is coded according to a predefined format and bit-rate. Then, this coded content is sent via internet. The audio/video bitstream is fragmented to a series of network packets, which are sent out to the user, via Internet protocol (IP) [,,]. The client can access to the video content via media player. This is an application that, while it memorizes a 978--79-33-9/8 $. 8 IEEE DOI.9/CERMA.8.93
video or audio segment (~ to seconds of content) [,,3], it display this information and so on. The video streaming architecture has two fundamental activities, see figure : ) digital content creation using compression techniques, ) content distribution via internet. The streaming server can store content and/or deliver it to the clients. It can stream two types of content: ) Streaming on demand The streaming server can stream data from media files physically present on the hard drive. The clients can request the content from the streaming server at any time. ) Streaming live The live event is captured and fed it into a compression platform, which compress the content. The streaming server wraps the compress signal in IP and transmits it over the internet in real time. RealVideo codec. The technical characteristics of this format are not public. This codec is suspected to be based on H.4 standard [,,]. Microsoft [3]: Microsoft Windows Media Encoder 9 Series 9...98 codec, VC- standard, SMPTE 4M [4]. Apple []: QuickTime 7 Pro codec, H.4 standard. 3.. Test sequence library The test sequence library is formed by 8 original video sequences in raw YUV 4:: format, see tables y. These sequences are widely used within of the video compression community due to their variational content of motion and texture. Table. Test sequences. Resolution: QCIF (7x44 pixeles). Application: video conference, video phone Sequence frames/seg. No. frames Carphone 3 38 Highway 3 Hall 3 3 Container 3 3 Table. Test sequences. Resolution: CIF (3x88 pixeles). Application: video web Sequence frames/seg. No. frames Foreman 3 3 Mobile 3 3 News 3 3 Stefan 3 9 3.. Coding process Figure. Video streaming architecture. 3. Evaluation methodology In the worldwide streaming media market there are many video streaming solutions. The leaders of such markets are RealNetworks, Microsoft, and Apple solutions. Each of one of these streaming solutions is a whole bundle which includes the streaming server, codec, and player. Due to the importance of these solutions today, is of the critical importance to evaluate and to freely report the performance of the following codecs: (the default parameters were used) The test sequences are coded at different bit-rates, see table 3. The principal video streaming formats are: Real Media (.rm), Windows Media (.wmv,.asf), and QuickTime (.mov). Table 3. Coding at different bit-rates. bit-rate (kbps) Resolution 4 8 3 7 QCIF CIF 3.3. Evaluation metric RealNetworks [9]: 3
The evaluation is based on the comparison of the three codecs. It consists to calculate the ratio between video quality and the bit-rate, as well as the ratio between rate compression and bit-rate in order to obtain the best codec. In order to compare the quality of the reconstructed video sequences, the PSNR (Peak Signal to Noise Ratio) [,7] was used (eq.). This criteria is the most widely used full-reference image quality measure in the image processing literature. At higher ratios, the image quality is increased. It is important to point out that sometimes the PSNR values do not necessarily match with subjective quality assessment. PSNR db = log N n ( ) NxM ( M X i, j Yi, j ) i = j = () Figure 3. Highway sequence. In equation, n represents the bit per sample, 8 bits in this case. NxM is the image resolution in pixels. X and Y are the original image and the reconstructed image respectively. 4. Experimental results In view of this encoding/decoding process, the following observations were obtained for each sequence the PSNR vs Bit-rate and Compression vs Bit-rate: Carphone: It presents a large facial motion. The codecs performance is shown in the figure. Figure 4. Hall sequence. Figure. Carphone sequence. Figure. Container sequence. Highway: It has the zoom camera. It presents a little texture in the background. The codecs performance is shown in the figure 3. 4
Hall: In this sequence is difficult to get robust estimates of the movement of the person who enters the corridor. The codecs performance is shown in the figure 4. Container: It depicts a ship moving slowly in the ocean. The camera moves in the same direction that the ship. The codecs performance is shown in the figure. In short, for the QCIF sequences, it is showed that the RealMedia codec has the best PSNR and compression performance at kbps. At bit-rate range of -3 kbps, the Windows codec has the best PSNR and compression, with exception in the Container sequence, which PSNR value is lower than the QuickTime codec. For higher bit-rates than 3 kbps, the QuickTime codec has the best PSNR value. However, it gives the worst compression ratio of all at this bit-rate. The RealMedia codec gives the best compression rate at this bit-rate, with exception in the Container sequence, which compression ratio is lower than the Windows codec. Figure 7. Mobile sequence. Figure 8. News sequence. Figure. Foreman sequence. Foreman: It contains different motion directions. It poses large facial motion and camera panning. The codecs performance is shown in the figure. Mobile: It has a lot of motion in the background with different motion directions. The codecs performance is shown in the figure 7. News: It consist of periodic background changes with news readers in the foreground. The codecs performance is shown in the figure 8. Stefan: It has very fast camera motions and the sportsman presents a non-rigid motion. The codecs performance is shown in the figure 9. Figure 9. Stefan sequence. In short, for the four CIF sequences, it is showed that at bit-rate range of -3 kbps, the RealMedia codec has the best PSNR value and compression ratio. However, at kbps for the Foreman and Stefan
sequences, the Windows codec hast the best PSNR value. At 8 kbps, the QuickTime codec gives the worst PSNR value. For higher bit-rates than 3 kbps, the Windows codec has the best PSNR value. However, it gives the worst compression ratio in most of the sequences, with one exception. For the News sequence, it presents the best compression ratio at higher bit-rates than kbps.. Conclusions The aim of this paper was to present and to discuss the performance of three principal commercial proprietary codecs used in the video streaming technology. The performance was examined, evaluating the tradeoff between compression rate and PSNR value for different transmission bit-rates. It was shown that at QCIF resolutions and a bit-rate of kbps, the RealMedia codec provided the best objective quality/compression rate tradeoff. The Window and RealMedia codecs are the best to use for bit-rates between and 3 kbps at QCIF CIF resolutions. They presented the best PNSR/compression rate tradeoff. The QuickTime codec is the best choice at higher bit-rates than 3 kbps, if a high objective quality is wished at QCIF resolution. However, if the high compression is the priority, the RealMedia codec is the adapted solution. For CIF video resolutions at higher bit-rates than 3 kbps, the Windows codec is the best choice for high PSNR. However, if the high compression is the priority, the RealMedia codec is the answers. Summary it is possible to conclude that the universal codec does not exist for any kind of sequence who shows the best PSNR value and compression rate at different bit-rates. Therefore, it is recommended to select a specific codec according to encoded content, bit-rate transmission and PSNR value/compression rate tradeoff wished.. Acknowlegment This work was realized under grant SIP834. 7. References [] Joe Follansbee. Get Streaming. Elsevier Inc. ISBN - 4-89-3. [] Wes Simpson. Video Over IP a practical guide to technology and applications. Elsevier Inc.. ISBN-3: 978--4-87-3. [3] http://en.wikipedia.org/wiki/streaming_media, (8). [4] Mireya S. García, Alejandro A. Ramírez. Video sobre IP: introducción do E.R.Académico. Tij, México. 3 Nov.. [] Starr Thomas, John M. Cioffi, and Peter J. Silverman. Understanding Digital Subscriber Line Technology. Upper saddle river, NJ: Prentice-Hall, Inc. 999. [] Oppenheim, Alan V.; Schafer, R. W.; and Buck, J. R. (999). Discrete-time signal processing. Upper Saddle River, N.J.: Prentice Hall. ISBN -3-749-. [7] http://en.wikipedia.org/wiki/video_on_demandn, (8). [8] Siyan, Karanjit. Inside TCP/IP, New Riders Publishing, 997. ISBN --74-. [9] http://www.realnetworks.com, (8). [] ITU-T Recommendation H.4 & ISO/IEC 449- (MPEG-4) AVC, Advanced Video Coding for generic Audiovisual Services, (version :3, versions : 4) version 3:. [] King N. Ngan, Thomas Meier and Douglas Chai. Advanced Video Coding :Principles and Techniques. Elsevier Science Inc., New York, NY, USA, 999. ISBN 44487X. [] Iain E. G. Richardson. H.4 and MPEG-4 Video Compression, Video Coding for Next Generation Multimedia. John Wiley & Sons, 3. ISBN-: [3] http://www.microsoft.com/en/us/default.aspx, (8). [4] SMPTE 4M, VC- Compressed Video Bitstream Format and Decoding Process. [] http://www.apple.com, (8). [] Stefan Winkler, Digital Video Quality,. Wiley, March. [7] Abdul H. Sadka. Compressed video communications. John Wiley & Sons, Ltd.. ISBN -47-843-8